The present invention relates to an isolator used in the microwave apparatuses. More specifically, the present invention relates to an isolator in which a ferromagnetic sheet (Sr-ferrite) together with an internal terminal sheet (with strip lines extending therefrom) and a garnet ferrite is inserted into a shielding case; dielectric devices and a chip resistor are installed on a PCB and around the shielding case; a connecting terminal sheet is formed; and thus the ferromagnetic sheet is securely placed by means of the strip lines of the internal terminal sheet and the garnet ferrite of the shielding case, so that the leakage magnetic flux shielding effect can be reinforced, that the bulk of the isolator can be made compact, that the assemblability can be improved, and that the manufacturing process can be simplified.
The generally known conventional isolator is inserted to between an antenna switch and a power amplifier module of a wireless apparatus, so that the signals reflected from the antenna switch are absorbed, thereby protecting the power amplifier module.
FIG. 1 is a block diagram of a system involving the isolator. As shown in this drawing, transmission signals Tx are amplified by a power amplifier module 15, are filtered by a low pass filter 14, and are sent through an antenna switch 12 to an antenna 11, so that the signals can be transmitted from the antenna 11.
Meanwhile, reception signals Rx are received by the antenna 11, and are sent through the antenna switch 12 to a band pas filter 16 so as to be filtered. Generally, an isolator 13 is disposed between the antenna switch 12 and the power amplifier module 15 of the wireless apparatus, so that the signals reflected from the antenna switch 12 can be absorbed, thereby protecting the power amplifier module 15.
FIG. 2 illustrates the basic equivalent circuit for the isolator. As shown in this drawing, an input terminal is coupled to an output part of the power amplifier module 15 of the transmitting part so as to receive the transmission signals Tx. Further, the input terminal block is connected an internal terminal block 22, and thus, the high frequency transmission signals Tx are transferred to the internal terminal block 22. An input capacitor C1 is connected between the input terminal block and the ground.
Further, an output terminal block is connected to the internal terminal block 22, while the other end of the output terminal block is connected to the antenna switch 12, so that the high frequency signals can be finally transmitted from the antenna 11.
An output capacitor C2 is connected between the output terminal block and the ground. A ground capacitor C3 and a longitudinal resistor R (50xcexa9) are connected in parallel between the internal terminal block 22 and the ground. The signals which have been transferred from the power amplifier module 15 through the input terminal block and the internal block to the output terminal block can reversely flow partly from the antenna switch 12. These returned signals are sunk into the ground from the internal block 22 through the longitudinal resistor R.
Therefore, the isolator 13 removes the power of the returning signals so as to ultimately prevent the power amplifier module 15 from being damaged by the power of the returning signals, thereby protecting the power amplifier module 15.
FIG. 3 is an exploded perspective view showing the constitution of the conventional isolator. As shown in this drawing, the isolator includes: an upper case 31; a ferromagnetic sheet (Sr-ferrite) 32 for generating a constant magnetic field; an internal terminal block 33 disposed under the ferromagnetic sheet 32, for generating an induced magnetic field, and including a garnet ferrite 42 and three strip lines 33xe2x80x2 connected to the input and output terminal blocks and to the ground; dielectric devices 35a-35c and a chip resistor 34 respectively connected to the three strip lines 33xe2x80x2 of the internal terminal block 33; an injection-molded case 36 having through holes 41 for fastening the internal terminal block 33, and having spaces for receiving the chip resistor 34 and the three dielectric devices 35a-35c, with input/output electrodes 38 and 39 and a ground electrode 37 being accommodated therein; and a lower case 40.
In this conventional isolator, the arrangement of the components is as follows. That is, the ferromagnetic sheet 32 and the garnet ferrite 42 are accommodated into the separate injection-molded case 36. Further, the three dielectric devices 35a-35c, the input/output electrodes 38 and 39, and the ground electrode 37 are horizontally arranged, and they are connected through the strip lines of the internal terminal block 33. Accordingly, the sizes of the dielectric devices, the chip resistor and the garnet ferrite are increased, and therefore, the overall bulk of the isolator is expanded.
Further, when the strip lines 33xe2x80x2 of the internal terminal block 33 are soldered to the dielectric devices 35a-35c and to the input/output electrodes 38 and 39, soldering defects are apt to occur due to the narrow space within the injection-molded case 36, as well as degrading the workability and the assemblability of the isolator, and making it impossible to obtain uniform products.
The present invention is intended to overcome the above described disadvantages of the conventional technique.
Therefore it is an object of the present invention to provide an isolator in which a ferromagnetic sheet is securely placed by means of strip lines of an internal terminal sheet and a garnet ferrite, thereby improving the shielding of the leakage magnetic flux to the degree of maximizing the shielding effect.
It is another object of the present invention to provide an isolator in which dielectric devices and a chip resistor are installed on a circuit board of the shielding case, thereby making the bulk of the isolator compact, making the response to the frequency easy, and making the characteristics of the product stable.
It is still another object of the present invention to provide an isolator in which the isolator can be easily installed on a circuit board, thereby improving the assemblability, and simplifying the manufacturing process.
In achieving the above objects, the isolator according to the present invention includes: upper and lower cases; a ferromagnetic sheet disposed within a shielding case, for generating a constant magnetic field; an internal terminal sheet having a plurality of strip lines for being connected to input/output electrode terminals and aground terminal and disposed under the ferromagnetic sheet and a garnet ferrite, the garnet ferrite being for generating an induced magnetic field; and the input/output electrode terminals and a chip resistor and three dielectric devices for being connected to the three strip lines of the internal terminal sheet, wherein the ferromagnetic sheet is inserted into the shielding case together with the garnet ferrite and the internal terminal sheet (with the strip lines extending therefrom), the shielding case is inserted into a lower metal case, the three dielectric devices and the chip resistor are installed on a circuit board and around the lower metal case, and a connecting terminal part having the input/output electrode terminals is formed.
In another aspect of the present invention, the isolator according to the present invention includes: upper and lower cases; a ferromagnetic sheet disposed within a shielding case, for generating a constant magnetic field owing to an input current; an internal terminal sheet having a plurality of strip lines for being connected to input/output electrode terminals and a ground terminal and disposed under the ferromagnetic sheet and a garnet ferrite, the garnet ferrite being for generating an induced magnetic field; and the input/output electrode terminals and a chip resistor and three dielectric devices for being connected to the three strip lines of the internal terminal sheet, wherein the ferromagnetic sheet is inserted into the shielding resin case together with the garnet ferrite and the internal terminal sheet (with the strip lines extending therefrom) and a plurality of insulating films, the shielding case is inserted into a lower metal case (serving as a ground), the three dielectric devices and the chip resistor are installed on a circuit board and around the lower metal case, and a connecting terminal part having the input/output electrode terminals is formed.